1. Field of the Invention
The invention relates to a novel process for producing an anisotropic magnetic material and an anisotropic magnetic material, and more particularly, to a process for producing an anisotropic magnetic material allowing the obtaining of an oriented magnetic bulk by combining an orientation step, in which an external field is imparted to a feebly magnetic material by using the feebly magnetic material as a starting material, and a reaction step, in which a material in an oriented state is transformed into a magnetic substance, and to an anisotropic magnetic material.
2. Description of the Related Art
In the related art, anisotropic magnets are produced by crushing and pulverizing ingots obtained by melting and casting a magnetic material in the form of a magnet raw material, molding the resulting fine particles in a magnetic field, and then sintering. In this case, since orientation is carried out in the solid phase, the degree of freedom in orientation of the fine particles is low and adequate orientation is impossible. In addition, since pulverization is carried out by crushing, it is difficult to obtain nanoparticles yielding nanocomposite magnets having a small particle size for use as high-performance magnets from the resulting fine particles. In addition, since a crushing step is required, there is a high likelihood of contamination by impurities due to mechanical contact. Moreover, in the case of oxygen-free magnets in the manner of Nd2Fe14B-based magnets, which are conventional as high-performance magnets, it is necessary to remove oxygen and other impurities introduced by oxidation and the like in the production process. On the other hand, in the case of bond magnets enabling control of orientation, heat resistance ends up decreasing considerably as a result of containing resin.
On the other hand, a process for producing a magnetic tape that forms a film in a magnetic field is a conventional technology for controlling orientation of magnetic materials. In this technology, the magnetic field is oriented after having coated magnetic fine particles onto a base film, and the resulting anisotropic magnetic material is limited to thin films having a film thickness on the micron order, thereby making it difficult to obtain bulk materials with this technology. In other words, bulk forms of magnetic materials obtained by forming magnetic fine particles into a film as described above cannot be used in applications other than magnetic tape, such as magnetic heads, high-frequency transformers or motors.
In addition to this orientation control technology using coating of magnetic fine particles and magnetic field orientation, an improved technology for improving orientation of nanoparticles in magnetic tape has been proposed (Japanese Patent Application Publication No. 2004-134040 (JP-A-2004-134040)).
In addition, iron oxide is a conventional example of a magnetic material for bulk materials containing oxygen (“Corrosion Preventive Technology”, Vol. 32, pp. 657-667, 1983), while soft ferrite is a typical example of a soft magnetic material, with MnZn ferrite represented by the formula MFe2O4 (M: Mn or Zn) being used in applications requiring high specific magnetic susceptibility and low coercive force (Hc), and Permalloy (78.5 Ni+Fe) or Supermalloy (5 Mo+79 Ni+Fe) and the like being used in applications requiring high magnetic permeability. Bulk materials in which orientation has been controlled are not conventional for this iron oxides and ferrite. In addition, these metals other than Fe, such as Mn, Zn, Mo and Ni, are elements having comparatively low Clarke numbers, which are used to quantify the level of mineral availability (for example, the Clarke numbers of these elements consist of 4.70 for Fe, 0.09 for Mn, 0.004 for Zn, 0.0013 for Mo and 0.01 for Ni).
On the other hand, a technology has been developed in recent years for producing bulk materials by controlling the orientation of feebly magnetic ceramic particles in an external field such as a magnetic field. For example, the related art disclosed in Japanese Patent Application Publication No. 2002-193672 (JP-A-2002-193672) is proposed as a slip cast molding technology in a magnetic field, while the related art disclosed in Japanese Patent Application Publication No. 2004-131363 (JP-A-2004-131363) is proposed as a magnetic field orientation electrophoresis deposition technology.
According to the improved technology described in JP-A-2004-134040, a nanoparticle magnetic recording medium is obtained in which L10-FePtCu or L10-FePt crystal grains are completely oriented along the c axis in a low melting point metal oxide or low melting point metal matrix by heat treatment and magnetic field orientation. However, the nanoparticles specifically described here are in the form of a thin film formed by sputtering, and the obtaining of a bulk material is impossible with this improved technology as well.
JP-A-2002-193672 describes an oriented ceramic sintered body and a production process thereof for sintering a molded article by dispersing a non-ferromagnetic powder having a non-isometric crystal structure in a slurry and then molding the slurry in a magnetic field. In addition, JP-A-2004-131363 describes a process for producing a ceramic high-order structure in which single crystal particles are oriented obtained by applying a strong magnetic field to a suspension of ceramic single crystal particles charged and dispersed in a solvent, orienting the individual particles by utilizing the crystal magnetic anisotropy thereof, applying an electric field to the suspension while in that oriented state and depositing the charged and oriented ceramic particles to obtain a ceramic structure in which the orientation and layer thickness of single crystal particles are highly controlled. According to these molding technologies, a bulk material in which crystallites are oriented in a fixed direction is obtained as a specific example thereof.
In this manner, a bulk structure in which magnetic particles are highly oriented in a fixed direction, or a production process thereof, are not yet conventional. Consequently, in order to form a bulk material from magnetic nanoparticles by applying orientation control technology for yielding a bulk material of ceramic particles to the magnetic nanoparticles, although it may be possible to consider orienting magnetic nanoparticles in the form of a slurry in a magnetic field as described in the related art, when the orientation of magnetic nanoparticles is attempted to be controlled in a magnetic field, magnetic interaction between the magnetic nanoparticles in the magnetic field increases, thereby making the magnetic nanoparticles susceptible to aggregation and making it difficult to obtain a bulk material in which orientation is controlled.
In other words, according to the related art, it has been difficult to obtain a bulk material in which the orientation of magnetic particles is controlled.